History of Rebreathers
1926 – The Draeger Company produce the “Badetauchretter”, a closed oxygen system utilising a breathing lung, chemical absorber and oxygen cylinder.
1939 – During the war years various oxygen Rebreathers are developed by the British, Italian and German Navies for mine-laying and manned-torpedo operations.
1952 – Working with the Draeger Company, Hans Hass develops the “Kleintauchgerät 138”
1953 – Appearance of the “Leutnant Lund II” oxygen Rebreather. A few of these units can still be found in working order!
1969 – Draeger launches the semi-closed “FertigGasTauchgerät” FGT-1 onto the market. Modified over the years, this unit is still used by military mine-laying divers.
1970 – W alter Stark produces the “Electrolung” – the first Rebreather controlled electronically.
1975 – The “LAR 5” (LungenAutomatisches Regenerationssystem), an oxygen Rebreather, is produced and exclusively designated for military special- forces activities.
1995 – The semi-closed Draeger “Atlantis” is launched onto the recreational diver market.
1998 – After undergoing an intensive 6 year development, the INSPIRATION Closed Circuit Rebreather becomes available to the recreational diving market. Continually upgraded since its launch, the INSPIRATION remains unparalleled as the only closed circuit Rebreather to satisfy the CE-norm requirements.
1999 The innovative significance of the INSPIRATION is recognised by its “product of the millennium” award and inclusion in the Millennium Dome exhibition in Great Britain.
1999-2009 The Inspiration is furthered developed. Improved “Vision” electronics, better sensors, an ADV, integrated deco-computer, CO2 monitoring and OBC.
General Principles of Rebreather Operation
If open circuit equipment is used, the diver receives fresh gas with every inhalation but exhaled gas is completely lost to the surrounding water. The amount of gas consumed is therefore dependant on the level of exertion and the depth of the dive.
However, the human body only needs a small amount of the oxygen part of the breathing gas to function; between 0.3 and 3.0 litres/min. depending on the level of activity. A large percentage of the gas supply is simply wasted. Furthermore, the wastage rises with increasing depth as the oxygen metabolised remains the same.
To more effectively utilise the gas supply and thereby increase the potential range of the dive, it is necessary to turn to so-called Rebreathers. These are available in semi-closed and fully closed versions.
A further difference lies in whether fresh gas is injected into the Rebreather mechanically or controlled by electronics. Electronically controlled units utilise dynamic gas mixing to provide the optimum gas mix at every depth.
Basically, all Rebreathers work in a very similar fashion. The breathing gas from a high pressure storage cylinder (normally a small standard diving cylinder), passes through an intermediate pressure reducing stage and then, via a constant flow valve, regulator or manual injection, into the breathing bag (counter lung). The diver inhales the gas from the counter lung. The expired gas is then directed via a one-way valve system through a chemical carbon dioxide filter (scrubber) that bonds with the exhaled carbon dioxide, removing it from the breathing loop. The metabolised oxygen is then replaced, either by constant flow (Semi-closed systems) or by injection as required (fully closed systems). A few fully-closed units, such as the INSPIRATION, inject oxygen after measurement by oxygen sensors, to maintain a constant, predetermined partial pressure of oxygen throughout the entire dive.
In the majority of units the supply of gas is automatically regulated. An additional bypass valve enables the diver to manually inject fresh gas. The direction of flow is controlled through the use of simple, reliable one-way valves (similar to the exhaust valve in a regulator second stage).
The most noticeable feature of a Rebreather, in comparison with an open circuit system, is the extremely economical gas consumption rate. This is why the Rebreather system is sought after by the technical diver.